The present application relates to a cable strand for the activation of electrically actuatable injection valves of internal combustion engines having a common-rail injection system, wherein the cable strand connects an engine control device with the injection valves, and wherein electrical cables of the cable strand are molded and/or foamed in a carrier that to a large extent prescribes the shape of the cable strand.
With modern self-ignition or compression ignition internal combustion engines, especially those used in commercial vehicles, increasingly fuel injection systems of the common-rail type are used. The advantage of such systems is that the pressurization is entirely decoupled from the injection process, as a result of which a plurality of partial injections can take place in a single injection cycle. To realize such partial injections, the electrically actuated injection valves that are disposed on the cylinder head must be activated several times in an injection cycle. In this connection, the activation is effected by means of an engine control system that, spaced from the injection valves, is disposed on the engine or in the engine compartment. For the connection of engine control unit and injection valves, a cable strand is used that, over a wide temperature range, must be provided with a lasting resistance to a variety of media, such as water, dirty water, salt water, water from high-pressure cleaners, cleaning fluid, fats, oils, fuels and the like. The lasting resistance is achieved in a known manner by encasing the conductor and plug connections with a correspondingly media-resistant polymeric material, or in the case of the plug connections with a media-resistant housing.
Due to the short switching or actuation cycles, with their steep signal amplitudes, and the considerable actuation currents that occur with common-rail injection systems, high-frequency actuation peaks result that, as interference radiation, are irradiated from the line connections between the engine control system and the injection valves. When such internal combustion engines are used in areas having increased requirements for a minimized interference radiation, additional measures are necessary in order to reduce this interference radiation to an acceptable level.
Two ways are customarily used to reduce interference radiation. One way provides for shielding the cable connections, thereby blocking the interference radiations the other way comprises providing the outputs of the engine control system with appropriate passive filter circuits that prevent the corresponding actuation peaks from passing to the cable connections.
Both possibilities have considerable drawbacks for use in commercial vehicles, especially those that are produced only in a small scale series for special applications. Where the cable strand is shielded, the entire cable strand, from the engine control system to the injection valves, must be provided with a metallic shielding. For this purpose, due to the aforementioned necessary lasting resistance against a number of media, the metallic shielding must be disposed below the casing of the cable strand that provides the lasting resistance. In addition, the shielding must be connected to the ground of the engine control system, at least at the ends of the cable strand. It will be readily appreciated that such an expensive modification of the cable strand for a small scale production is precluded as unacceptable for cost reasons.
A modification of the engine control system would also require considerable expense, assuming these measures would even be possible due to technical conditions, such as available space in the housing of the engine control system, the development of heat etc.
Proceeding from this situation, it is an object of the present application to realize a straightforward and hence economical possibility for eliminating the undesired interference radiation.